Electron tube



Aug. 30, 1938. w. DALLENBACH ELECTRON TUBE Filed Jan. 25, 1935 Fig". 3b

REE. l

A. lnventor:

Patented Aug. 30, 1938 UNITED STATES PATENT OFFICE ELECTRON TUBE Walter Dillenbach, Berlin-Charlottenburg, Germany, assignor to the firm N. V. Machinerieenen Apparaten Fabrieken MeaP',

erlands Utrecht, Neth- 8 Claims.

The present invention relates to an electron tube for exciting i. e. generating, amplifying and receiving ultra-frequency electro-magnetic oscillations, particularly of oscillations possessing a wavelength of less than one metre. The electron tube in accordance with the present invention belongs to that type of high vacuum electron tube in which the flow of electrons passing over between the cathode and the positive electrode, is controlled by means of a grid being positioned in-between. In consequence of the employment of the control-grid in such tubes, the field space between the cathode and the positive electrode is divided into two spaces, 1. e. in a control space situated between the cathode and the grid and an exciting space situated between the grid and the anode. For the purpose of being able to excite oscillations, the duration of transmission of the electrons from the cathode to the anode must remain short or, at least comparable in relation to the period of the oscillation to be excited. In connection with the excitation of oscillations possessing a wavelength of less than one metre and with a clearance between the electrodes practically possible, such high anode potentials are necessary, that in consequence of the magnitude of the anode through the control grid, the tube will no longer be able to work in the space charge zone and thus lose its controlling property.

This difiiculty has been obviated in accordance with the present invention by the fact that for the purpose of exciting ultra-high frequency electro-magnetic oscillations, particularly such pos sessing a wavelength of less than one metre, electron tubes are being employed, in which, between the control grid and the anode, a further grid with a high positive charge has been provided. As a result of the introduction of this so-called acceleration grid, three spaces will be produced between the electrodes, viz. a control space between the cathode and the control grid, an acceleration space between the control grid and the acceleration grid and an exciting space between the acceleration grid and the anode.

In the acceleration space, the velocity of...the electrons is raised to such an extent, that they are made to cross the space, intended for the excitation of the ultra-high frequency oscillations and situated between the acceleration grid and the anode, at intervals of time which are short or comparable with .the period of the oscillation to be excited. It is advisable to keep high-frequency fields away from the acceleration space. The interval of time of the electrons in this space and, therefore, also the distance from the control grid and acceleration grid, will then, be without infiuence'upon the excitation. The clearance between the control grid and the acceleration grid can, in accordance therewith be made to be so large, that also in connection with high potentials at the acceleration grid the saturation of the emission has not yet been attained and that, therefore, the control grid still possesses its controlling properties. Furthermmore, it will now be possible to adapt path of transmission and duration of transmission to the period of the oscillation to be excited, without exercising a deleterious influence upon the control space.

The electron tubes in accordance with the present invention may be provided not only with plane, but also with concentric and, finally, also with cylindrical electrodes. The arrangement may, furthermore, be of such a nature, that the control space limited by the cathode and by the control grid, may be made to belong to a control resonator, and the exciting space, limited by the acceleration grid and the anode, to an exciting resonator. The acceleration space between the control grid and the acceleration grid suitably remains alternating-field-free, whereby disturbing influences upon the excitation will be obviated. If the control resonator and the exciting resonator are coupled with each other, a reduction of the damping of the resonators may be attained, in consequence of which the arrangement as amplifier will attain a higher amplification, as receiver a higher sensitivity and, finally, it may, in connection with excitation beyond the commencement of the oscillations, be used as generator.

The Figs. 10. and 1b to 3a and 3b represent three examples of performance of the present invention,

Fig. 1b is a longitudinal section through an arrangement of the invention in which plane electrodes are used, and Fig. 1a is a section through 1b along line la, la. Lecher systems have been provided to serve as resonators, said Lecher systems being open at the ends and consisting of plane metal bands.

Fig. 2b is a longitudinal section through an arrangement of the invention in which concentric and cylindrical electrodes are used, and Fig. 2a is 50 a section through Fig. 2b along line 2a, 2a. The resonators have been adapted to the electrodes and are each made to consist of a concentric and cylindrical Lecher system.

Figs. 3a and 3b are made to show, in cross section as well as in longitudinal section, an arrangement, well screened to prevent the escape of loss radiation, the electrodes of which arrangement are also of the cylindrical and concentric type. Fig. 3a is a cross section along line 3a, 3a of Fig. 3b. The electrodes have been extended at either end by means of tubes, thus producing two concentric resonance spaces, the ends of which have been closed up by short-circuit condensers. The arrangement is, moreover, connected with an aerial over an energy line.

In the first instance the present invention will be described in detail, reference being had to Figs. la and 1b in connection herewith:

In the electron tube, illustrated in Figfour plane electrodes have been accommodated within the vacuum vessel I, viz. a cathode 2, a control grid 3, an acceleration grid 4 and an anode 5. The heated wire 6 placed within the cathode serves as a source of electrons. The cathode 2 and the control grid 3 have been extended by two parallel metallic bands I, 8, so as to form an open Lecher system. In an identical manner have the acceleration grid and the anode been continued by metallic bands 9, I0, being parallel to each other, thus also forming an open Lecher system. If an open Lecher system of this description is excited in the first harmonic, a potential node will be formed in the central portion of the conductors and potential loops at the ends. The length of the conductors will then coincide with half the wavelength of the oscillation. In order to avoid disturbances of the alternating fields, the metallic bands are made to intersect the vacuum vessel in the potential node. The walls of the vacuum vessel are, for this reason, fused with the metallic bands, so as to be vacuum-tight, approximately in the electric centre. Thus one half of the Lecher system is situated without, i. e. outside of the vacuum vessel, whereas the other half has been accommodated inside said vacuum vessel. The battery H is utilized as current source for heating the hot heating wire 6. With the aid of the battery I! a bias is produced at the control grid 3, and through the medium of the batteries 13 and M a suitable potential'is imparted to the acceleration grid and the anode. The potential leads are connected in the proximity of the potential nodes, i. e. in the proximity of the fusing points, with the metallic bands I, 8 or 9, l0, galvanically joined with the electrodes, with the result that leakage losses over the lead are being avoided. The two Lecher systems i, 8 and 9, l0, have been so arranged relatively to each other, that the acceleration space positioned between the control grid 3 and the acceleration grid 4, is situated far beyond the resonance of the oscillation to be excited or to be amplified. In the instance referred to, the two Lecher systems extend from the electrodes in opposite directions.

The arrangement specified previously may be employed for the purpose of exciting, particularly, however, for the amplification of oscillations, if the following directions are observed.

The control grid is suitably given a weakly negative bias in order to avoid an additional damping of the control resonator. Furthermore, so as to make low control alternating potentials do, it is advisable, to select the clearance between the'hot cathode and control grid as narrow as possible, with the aim of obtaining in the control space, durations of transmission of the electrons which are short when compared to the duration of oscillation. If the duration of transmission of the electrons in the control space is short when compared to the duration of oscillation, the displacement current in the control space, produced by the controlled electron alternating current, and also exercising a damping ef feet on the control resonator, will be negligibly small. With regard to the short duration or transmission in the control space it will be of advantage to cause the potential of the acceleration grid to be so high, that the tube works in the proximity of the upper end of that part of the static characteristic rising linearly. Experiments in connection with a wavelength of 12 cm. have proved, that at such a selection of the potential of the acceleration grid, the dynamic characteristic deviating from the static characteristic, presents its maximum slope. Also when employing the arrangement as rectifier, particularly as audion, the rectification at the upper bend of the static characteristic will be more effective than the rectification at the lower bend, in consequence of the short duration of transmission of the electrons in the control space.

It has further been proved, that the electron alternating current, produced in the control space, is first made to acquire a considerable velocity in the acceleration space, in consequence of the high positive potential of the acceleration grid and subsequently brings about an optimal excitation,'if the anode potential is selected in the proximity of the cathode potential. This means, however, that the electrons must arrive at the anode at the velocity zero. This relation exists practically independent of the velocity with which the electrons enter the excitation space. By means of experiments it has been ascertained to be essential with maximum excitation that the anode potential be selected to be a little less positive than the potential of the cathode. In spite thereof, however, the majority of the electrons describe a turning movement in front of the anode and return to the acceleration grid. This reversal is a result of the fact, that the electrons are subjected to lateral deviations through the medium. of the bars of the acceleration grid 4 which impart to them a velocity component parallel to the grid and reduce the velocity component vertical to the grid. The reason, why an electron alternating current, turning back just in front of theanode, exercises a maximum excitation upon a resonator coupled with the excitation space, is explained by the fact, that at this selection of the anode potential the electrons are the longest time in interaction with the high frequency field in the excitation space. The coupling between the moved electrons and the high frequency field will then be at its maximum. If

the anode potential is selected so as to be essen-.

tially more positive than the cathode potential, the duration of transmission will be reduced and the electrons received by the anode after once crossing the excitation space. If, however, the anode potential is selected so as to be essentially more negative than the cathode potential, the electrons will be forced to return in a plane between the acceleration grid and the anode. Their duration of transmission in the excitation space will again be shorter than in the most favourable case, in which the reversal takes place immediately in front of the anode.

The optimum of the excitation effect on the excitation space presenting itself at the selection of the anode potential depends now, on the one hand, upon the velocity at which the elec tron alternating current is made to pass through the acceleration grid 4. If in connection with plane electrodes and a neglected effect of the space charges in the excitation space the anode potential is selected so as to be in the proximity of the cathode potential, it will be found that with a change of the acceleration potential the exciting effect will then become a maximum, if the electrons, turning back immediately in front of the anode, are made to cross the exciting space at a simple duration of transmission which is shorter than half the duration of the period and approximately equals one third of the duration of period of the ultra-high frequency oscillations.

In connection with an arrangement which is not plane, but, for instance, cylindro-symmetrical or, in due consideration of the space charges, 1. e. in case of high current density in front of the anode, it is necessary to so adjust the simple duration of transmission that it deviates somewhat from one third of the duration of period of the ultra-high frequency oscillations.

The most simple method is to determine in each case by means of practical experiments the potentials and therewith the duration of transmission, at which maximum excitation, e. g. in case of an oscillation generator, maximum oscillatory power presents itself.

' If to the end, situated outside the vacuum vessel, of the control resonator i, 8, ultra-high frequency alternating potentials are conveyed and the D. C. potentials of the electrodes are adjusted in such a manner, that a maximum control effect upon the stream of electrons emanating from the cathode, will take place, as well as a maximum excitation of the electron alternating current passing through the acceleration grid into the excitation space, the output of the exciting resonator 9, I will be intensified.

Instead of the plane arrangement represented in Figs. 1a and 1b, a cylindro-symmetrical arrangement, shown in Figs. 2a and 2b, may be ad vantageously made use of. In this instance, the electrode system consists of a wire or bar-shaped hot cathode l5 and the other electrodes concentrically surrounding the cathode i. e. the control grid Hi, the acceleration grid 11 and the anode l8. The cathode l5 and the control grid l6 have been extended on the left-hand side through the medium of the two metallic tubes 19, 26, so as to form a cylindrical Lecher system serving as control resonator. The acceleration grid l1 and the anode l8 have also been continued so as to form just such a cylindrical and concentric Lecher system by means of the two metal tubes 2|, 22. The arrangement has been accommodated completely within the vacuum vessel I. The D. C. leads have been provided in the centre of the Lecher system in potential nodes. The control energy may be conveyed to terminals 23 pro vided outside the vacuum vessel and the enhanced output may be taken from the terminals 24. The represented, cylindrical arrangement is characterized, when compared to the plane arrangement, by an inconsiderable damping capacity, which may be particularly attributed to the low leakage loss.

The arrangements represented by Figs. 1a and lb or 2a and 2b are particularly adapted for the amplification of decimetre and centimetre waves. A coupling between the control resonator and the exciting resonator has not been provided for in that case. If, however, the exciting space and the control space are coupled in such a manner that, for instance, a part of the enhanced output bodies 28 and 28.

is conveyed phase-correctly to the control resonator, it will be possible to attain a reduction of the damping of the whole of the oscillatory arrangement. If the reduction of damping is effected in the proximity of self-excitation, the arrangements will represent highly sensitive resonance amplifiers and are excellently adapted for receiving ultra-high frequency oscillations. If the reduction of the damping property is increased up to the self-excitation of oscillations, the arrangement represents a generator, which may be used for the emission of oscillations. It is, however, a matter of course, that the coupling of the two resonators and the duration of transmission of the electrons from the cathode to the entrance into the exciting space are so adapted to each other, which may be suitably attained by changing the acceleration potential or by the suitable selection of the clearance between the control grid and the acceleration grid, that the controlled stream of electrons enters the exciting space with a phase which proves most suitable for excitation purposes.

An arrangement of suchdescription has been reproduced in the Figs. 3a and 3b, adapted for transmitting and receiving ultra-short wave 05- ciliations. The electrode system consists in this instance, identical with that arrangement shown in Figs. 2a and 2b, of a bar-shaped hot cathode l5 and the cylindrical and concentric electrodes surrounding the cathode, viz. the control grid It, the acceleration grid I! and the anode l8. All four electrodes have been extended at either end by means of metallic conductors, i. e. the cathode by the rods 25 and 25, serving for the conveyance of the heating current, the control grid through the medium of the two cylindrical tubes 26 and 26' and the acceleration grid by means of the two cylindrical tubes 21 and 21'. The anode I8 has likewise been extended at both ends so as to form a cylinder, enclosing the previously mentioned electrodes with their extensions. The space between the tubes 26 and 21 or 26' and 21' has been filled up by means of two insulating With the aid of these insulating bodies, the tubes connected with the control grid and the acceleration grid have been supported against each other, whilst in addition thereto the acceleration space, extended towards both sides, is detuned relatively to the natural frequency of the resonators provided within the tube. The control resonator is limited by the surface of the rods 25, 25' and of the cathode, as well as by the interior surfaces of the control grid l6 and the tubes 26 and 28', the exciting resonator, on the other hand, being limited by the exterior surfaces of the acceleration grid l1 and the two tubes 21 and 21' and by the inner face of the extended anode l8. The ends of the Lecher system are provided with short-circuit condensers for the oscillation. The tubes 26 and 26 are each provided at their free end with a flange 29 and 29', forming, together with the plates 30 and 30 a short-circuitpondenser each.

In an identical manner has the left end'of the extended anode tube l8 been provided with a flange 3| which, in conjunction with the plate 36 also forms a short-circuit condenser. At the right side the extended anode has been continued by the tube 32 and forms, together with the extension 33 of the tube 21', an energy line. The inner conductor 33 of the energy line' further passes on the right side into the aerial 34, whereas the outer conductor 32 of the energy line, terminates in the metal plate 35 serving as counter poise. The aerial 34 is thus made to project freely "beyond the metal plate 35 into the space.

The tube, which has been represented in Fig. 3 does not require a vacuum vessel if, as may be seen from Fig. 3b, the interspaces between the metallic parts surrounding the tube, have been closed up and rendered vacuum-tight by glass-fusings. Thus the two plates 30 and 3| have been connected by means of a glass seam 36 and the right end of the tube 32, 33, serving as energy line, by means of a glass seam 31, so as to be vacuumtight. The current and potential leads have been joined to the electrodes in the proximity of the short-circuit condenser, for the purpose of keeping the leakage losses within the smallest possible limits. In view of the fact that the cylindrical resonators are excited in the first harmonic, in connection with which potential nodes are formed at the ends and a potential loop in the centre, the total length of the resonators is to be made to equal half the wavelength of the desired oscillation. The energy line and the aerial are suitably given a length which equals a quarter wavelength of the oscillation. The optimal coupling of the emitter to the exciting resonator is obtained by means of a proper selection of the space between the cylinders 32 and 33. The closer the space between the two cylinders, the looser will be the coupling between the emitter and the exciting space. It is advisable to so adjust this coupling, that the emitter represents for the resonator of the exciting space an optimal loading resistance.

In the represented example of performance, the condenser plate 30, closing up the control resonator situated in the proximity of the axis, as well as the peripherally placed exciting resonator, is eifective in bringing about the coupling of the two resonators. The closer the space between this plate 30 and the flange 29, the greater the capacity of this short-circuit condenser and, similarly, the smaller will be the coupling between exciting space and control space. It now the hot cathode I5 is heated and if the other electrodes, as already mentioned. are given a suitably selected continuous potential and, furthermore, if the control grid is given a weakly negative, the acceleration grid a high positive and the anode a weakly positive continuous potential relatively to the cathode, the ultra-high frequency alternating potentials produced at the electrodes in the exciting space, will be transmitted to the control resonator over the coupling channel existing between 29 and 30. In consideration of the fact, that the control resonator is incapable of emitting loss leakage, it possesses a very small natural damping; for this reason it will also be possible, in connection with a weak coupling with the exciting resonator, for high alternating amplitudes to present themselves between cathode and control grid, in consequence of which the stream of electrons, emanating from the cathode, is vigorously controlled through.

What I claim is:

1. A high frequency arrangement comprising an electron tube having at least four electrodes,

and including two grid electrodes within said tube, two oscillatory systems, each of said systems containing one of said grid electrodes and extending in a direction opposite to the other system, each two other of said electrodes being connected to one of said systems, each system being .formed of at least two tubular conductors, one of which is within the other, said grids being continuations of the conductors belo to said systems, and each grid section being spaced frqm and extending substantially coincidental with each other grid section.

2. An arrangement as in claim 1, said grid electrodes comprising a control electrode, and an accelerating electrode, and said other electrodes comprising an anode and a cathode, means to impress a negative potential on said control electrode with respect to said cathode, means to impress apositive potential on said anode with respect to said cathode, and means to impress a higher positive potential on said accelerating electrode with respect to said cathode.

3. An arrangement as in claim 1, said other electrodes comprising a cathode and an anode, and lead wires for said electrodes, said wires being connected to said oscillatory systems at potential node points.

4. An arrangement as in claim 1, said other electrodes comprising a cathode and an anode, short circuit condensers, said condensers sealing the ends of said oscillatory systems, and means coupling said condensers to each other, whereby said systems are sealed against radiation losses.

5. An arrangement as in claim 1, said other electrodes comprising a cathode and an anode, and means coupling said oscillatory systems to each other.

6. An arrangement as in claim 1, said other electrodes comprising a cathode and an anode, short circuit condensers, said condensers sealing the ends of said oscillatory systems, an extension on one of said conductors of an oscillatory system, said extension comprising an energy lead coupled with a radiator.

7. An arrangement as in claim 1, .said electrodes comprising a cathode and an anode, short circuit condensers, said condensers sealing the ends of said oscillatory systems, said condensers being each composed of two plates, a plate of one condenser being electrically connected to a plate of the other condenser, an extension on one of said conductors of an oscillatory system, said extension comprising an energy lead and an aerial, and a plate connected to and perpendicular to said extension forming a counterpoise for said aerial.

8. An arrangement as in claim 1, said other electrodes comprising a cathode and an anode,

. short circuit condensers, said condensers sealing the ends of said oscillatory systems, said condensers being each composed of two plates, one of the plates of a condenser and an electrode forming a part of the outside walls of said electron tube.

WALTER Dir-[mason u 

